Computer assisted analysis of fetal age in the third trimester using multiple fetal growth parameters.

A new technique is described for predicting menstrual age in the third trimester of pregnancy (28-42 weeks) using multiple fetal growth parameters (biparietal diameter, head circumference, abdominal circumference, femur length). Evaluation of this technique in 177 normal third trimester pregnancies demonstrated that significant improvement in the variability in predicting menstrual age can be achieved when two or more parameters are used collectively instead of a single parameter used individually. The optimal combination prior to 36 weeks was biparietal diameter, abdominal circumference, and femur length, while after 36 weeks the optimal combination was head circumference, abdominal circumference, and femur length. The use of these combinations resulted in smaller mean errors, standard deviations, and maximum errors. Regression equations and tables of normal values are provided to facilitate the use of this dating method.